In typical large sized display devices, there are LCD (Liquid Crystal Display device) and PDP (Plasma Display Panel).
Different from the PDP which is a spontaneous emission type, the LCD, having no light emitting device for itself, requires a separate backlight unit, essentially.
Depending on a position of a light source, in the backlight units used in the LCD, there are an edge type backlight unit and a direct type backlight unit. The edge type backlight unit has the light source disposed at left/right sides or upper/lower sides of an LCD panel, and a light guide plate for uniform diffusion of a light throughout the panel to have good uniformity of the light and to enable to fabricate an extra thin panel.
The direct type, a technology generally applied to a display device larger than 20″, has a plurality of light sources disposed on an underside of the panel, to have better light efficiency than the edge type, finding its application to a large sized display device which requires high brightness.
As the light source for the related art edge type or the direct type backlight unit, CCFL (Cold Cathode Fluorescent Lamp) has been used.
However, the backlight unit of the CCFL has drawbacks in that a substantial amount of power is consumed by the CCFL since the CCFL requires the power applied thereto always, a color reproduction ratio is poor to be about 70% of the CRT, and environmental pollution is caused by mercury added thereto.
In order to resolve above problems, as a substitute for the CCFL, active researches on a backlight unit of LED (Light Emitting Diode) are being made, presently.
The backlight unit of LED enables partial turn on/off of an LED array to permit significant reduction of power consumption, and the backlight unit of R,G,B LED provides color reproduction exceeding 100% of the color reproduction range specification of the NTSC (National Television System Committee), thereby allowing providing an excellent picture quality to the consumers.
Moreover, the LED fabricated by a semiconductor process is not harmful to the environment.
Though there are LCD products having the LED applied thereto with above advantages being released all the time, since a driving mechanism thereof is different from the related art CCFL light source, drivers, PCB (Printed Circuit Board), and the like are expensive.
Accordingly, the LED backlight unit is applied to expensive LCD products only, yet.
FIG. 1 illustrates a cross-sectional view of a related art two edge type backlight unit.
Referring to FIG. 1, the backlight unit is provided with an optical member 10, a cover plate (Or, heat bar) 20, first and second reflectors 30 and 32, a light source module 40 having a light source 42 and a circuit board 44, and a bottom chassis 50 for supporting the second reflector 32.
The cover plate 20 holds the light source module 40, and has a connection portion 24 coupled to a connection portion of the bottom chassis 50. And, the cover plate 20 dissipates heat from the light source module 40 to an outside of the backlight unit through heat dissipation fins 22. The optical member 10 is placed on the cover plate 20.
Consequently, the related art backlight unit has a problem in that the heat from the light source module 40 is transferred to the optical member 10 through the cover plate 20, to deform the optical member 10.
And, the first reflector 30 is attached to a part of the cover plate 20 adjacent to the light source module 40. Since the part of the cover plate 20 to which the first reflector 30 is attached is narrow and recessed, with making attachment of the first reflector 30 difficult, the working efficiency is poor.